65 research outputs found
Genetic Variation of Juvenile Wood Properties in a Loblolly Pine Diallel Test
The reduced rotation age for loblolly pine plantations has resulted in an increased percentage of juvenile wood. Juvenile wood has lower wood density, shorter tracheid length and higher lignin content than mature wood. The increased use of juvenile wood has reduced yields and increased pulping costs for the pulp and paper industry. If significant genetic variation in juvenile wood properties can be found, breeders may be able to improve juvenile wood properties to reduce pulping losses. Genetic variation in several wood quality traits of loblolly pine (Pinus taeda L.) was investigated for 14 full-sib families generated by a 6-parent half-diallel mating design. Wood samples of 12 mm increment cores were collected from 11-year-old trees from one test site. Earlywood and latewood of ring three (juvenile wood) and ring eight (transition wood) for each increment core were analyzed for alpha cellulose content (ACY), average fiber length (FLW), coarseness (COA), and lignin content (LIG). Ring three and ring eight had significant differences in ACY, FLW, and COA, but not for LIG. Latewood of both rings had higher ACY, FLW, and COA than earlywood. Transition wood had significantly higher ACY, FLW, and COA, but lower LIG than juvenile wood. Families differed significantly for ACY, FLW, and COA, but not for LIG. In general, additive genetic effects explained greater percentages of family variation than dominance genetic effects. Genetic variation increased from juvenile to transition wood. While weak individual and family heritabilities were found for ACY, FLW, and COA for juvenile wood, heritability estimates for transition wood were moderate, indicating the potential for improving these juvenile traits.Papers and abstracts from the 27th Southern Forest Tree Improvement Conference held at Oklahoma State University in Stillwater, Oklahoma on June 24-27, 2003
Bimodality and Gaps on Globular Cluster Horizontal Branches. II. The Cases of NGC 6229, NGC 1851 and NGC 2808
The outer-halo globular cluster NGC 6229 has a peculiar horizontal-branch
(HB) morphology, with clear indications of a bimodal HB and a ``gap" on the
blue HB. In this paper, we present extensive synthetic HB simulations to
determine whether peculiar distributions in the underlying physical parameters
are needed to explain the observed HB morphology. We find that a unimodal mass
distribution along the HB can satisfactorily account for the observed HB
bimodality, *provided* the mass dispersion is substantially larger than usually
inferred for the Galactic globular clusters. In this case, NGC 6229 should have
a well-populated, extended blue tail. A truly bimodal distribution in HB masses
can also satisfactorily account for the observed HB morphology, although in
this case the existence of an extended blue tail is not necessarily implied.
The other two well-known bimodal-HB clusters, NGC 1851 and NGC 2808, are
briefly analyzed. While the HB morphology of NGC 1851 can also be reproduced
with a unimodal mass distribution assuming a large mass dispersion, the same is
not true of NGC 2808, for which a bimodal, and possibly multimodal, mass
distribution seems definitely required.
The problem of gaps on the blue HB is also discussed. Applying the standard
Hawarden (1971) and Newell (1973) chi-squared test, we find that the NGC 6229
gap is significant at the 99.7% level. However, in a set of 1,000 simulations,
blue-HB gaps comparable to the observed one are present in ~ 6 - 9% of all
cases. We employ a new and simple formalism, based on the binomial
distribution, to explain the origin of this discrepancy, and conclude that
Hawarden's method, in general, substantially overestimates the statistical
significance of gaps.Comment: 50 pages (includes 5 tables and 18 multi-panel figures).
Higher-resolution versions of Figs. 15a and 15b are available from the first
author upon request. To appear in The Astrophysical Journa
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